The present invention relates to an ink supply system, such as an ink supply system for an inkjet printhead.
In order to increase the speed of inkjet printing, inkjet printheads are typically provided with an increasing number of ink ejection channels. For example, there are commercially available inkjet printheads having in excess of 500 ink ejection channels, and it is anticipated that in future so called xe2x80x9cpagewide printersxe2x80x9d could include printheads containing in excess of 2000 ink ejection channels.
During inkjet printing, the quality of printing has been found to deteriorate due to a number of problems associated with the supply of ink from an ink reservoir to the printed page, for example, due to blockage of the nozzles of the printhead and drying of ink on the nozzle plate.
Various solutions to these problems have been proposed, including capping, wiping of the nozzle plate and xe2x80x9cpurgingxe2x80x9d of the ink in the printhead by forcing ink from all of the nozzles to clear blockages in the ink supply to the nozzles. However, such a purging mechanism can result in the wastage of a large volume of ink, particularly in pagewide printers, if not all of the nozzles have ejection problems.
In at least its preferred embodiment, the present invention seeks to solve these and other problems.
In a first aspect, the present invention provides an ink supply system for supplying ink to a printhead, said system comprising:
at least one ink manifold comprising a plurality of outlets for supplying ink from the manifold to said printhead; and
means for selectively applying or increasing a pressure difference of an ink flow from at least one of the outlets to the printhead.
By selectively increasing the pressure of ink from at least one of the outlets to the printhead, localised higher-pressure purging of the printhead can be achieved than if the pressure of the ink flow from all of the outlets was the same. The ink supply may be pumped or gravity fed, and housekeeping routines can be conducted where ink is forcibly ejected through selected sections of the printhead. A higher ejection pressure in sections to be purged can therefore be achieved, and the amount of ink ejected during housekeeping can also be reduced.
In one preferred arrangement, the means for selectively increasing the pressure of ink from at least one of the outlets to the printhead comprises means for selectively substantially blocking the flow of ink from at least one of the outlets to the printhead to increase the pressure of the ink flow from an unblocked outlet to the printhead.
The ability to block off areas of the printhead from the ink supply can improve the priming and filling ability of the printhead. Printheads are generally supplied empty and need to be filled when installed, which can often lead to air being entrained within the printhead. Filling has previously been conducted by attaching a cap to the front face of the head and sucking the air from the printhead through the cap until ink flow from the nozzles is detected. Selectively blocking of one or more of the outlets can enable individual sections of the printhead to be primed in turn.
Thus, in a second aspect the present invention provides an ink supply system for supplying ink to a printhead, said system comprising:
at least one ink manifold comprising a plurality of outlets for supplying ink from the manifold to said printhead; and
means for selectively substantially blocking the flow of ink from at least one of the outlets to the printhead in order to supply ink from an unblocked outlet to the printhead.
Preferably, the blocking means comprises at least one valve for selectively closing at least one of the outlets in order to supply ink from an open outlet to the printhead. Valves can be closed to channel ink into a particular section of the printhead or open to ensure that ink flows through the whole printhead. Selective opening and closing of the valves can facilitate vacuum filling of the printhead with ink. The printhead is typically vacuum filled by the application of a cap attached to a vacuum source to the front face of the printhead. A vacuum is applied to the head to exhaust air, and then the valves are quickly opened to allow ink to enter the printhead. Should air be trapped within a section of the head, particular attention can be given to this section by selectively closing a number of the valves. Preferably, the at least one valve is housed within the or each manifold.
The system may comprise a plurality of valves, each outlet being selectively closable by a respective valve. This can enable more selective opening and closing of the outlets of the manifold. The system may comprise a single manifold, or alternatively a plurality of manifolds for supplying ink to the printhead.
Means are preferably provided for supplying ink to the or each manifold. The ink supply means may comprise an ink reservoir for storing ink, and a pump for pumping ink from said reservoir to the or each manifold. The pump is preferably a diaphragm pump which, being essentially one-way, can ensure that any localised increase in the pressure of the ink flow to the printhead does not permeate back to the ink reservoir.
The ink supply means preferably comprises a tank for receiving ink supplied from said ink reservoir and supplying the received ink to the or each manifold. Ink flow through the tank is preferably arranged to reduce output pressure variations caused by fluctuations in the inlet pressure resulting from operations of the pump. The pressure purging routine is preferably instigated by the injection of ink into the tank. A valve may be provided for selectively connecting the tank to the reservoir to regulate the volume of ink in the tank. The tank may comprise means for indicating the volume of ink in that tank, for example, means for indicating the level of ink in the tank.
Instead of a single ink reservoir for storing, for example, black ink, the ink supply means may comprise a plurality of ink reservoirs for storing ink, the ink supply means being arranged to supply ink from each reservoir to at least one manifold. Preferably, each reservoir stores ink of a respective colour. For example, four reservoirs may be provided for storing black, cyan, yellow and magenta ink respectively.
With such a plurality of ink reservoirs, the ink supply means may comprise a plurality of pumps, each pump being arranged to pump ink from a respective reservoir to the at least one manifold, may comprise a plurality of tanks, each tank being arranged to receive ink supplied from a respective ink reservoir and supply the received ink to said at least one manifold, and may comprise a plurality of valves, each valve being arranged to selectively connect a respective tank to a respective reservoir to regulate the volume of ink in that tank.
The ink supply system suitably comprises means for filtering ink output from the or each manifold to the printhead.
The present invention extends to an ink supply system as aforementioned for supplying ink to a plurality of printheads.
In a third aspect, the present invention provides a method of supplying ink to a printhead, said method comprising the steps of:
providing at least one ink manifold comprising a plurality of outlets for supplying ink from the manifold to said printhead; and
selectively applying or increasing a pressure difference of an ink flow from at least one of the outlets to the printhead.
In a fourth aspect, the present invention provides a method of supplying ink to a printhead, said method comprising the steps of:
providing at least one ink manifold comprising a plurality of outlets for supplying ink from the manifold to said printhead; and
selectively substantially blocking the flow of ink from at least one of the outlets to the printhead in order to supply ink from an unblocked outlet to the printhead.
In a fifth aspect, the present invention provides a method of supplying ink to a printhead, said method comprising the steps of:
providing at least one ink manifold comprising a plurality of outlets for supplying ink from the manifold to said printhead; and
substantially blocking the flow of ink from said outlets to the printhead;
creating a pressure differential between said printhead and said at least one manifold; and
selectively unblocking the supply of ink from said outlets to enable ink to be supplied under said pressure differential to the printhead.